A three-judge panel of the court said the proof-of- citizenship requirement conflicted with the intent of the federal law aiming to increase voter registration by streamlining the process with a single form and removing state- imposed obstacles to registration.

The federal law requires applicants to “attest to their citizenship under penalty of perjury” without requiring documentary proof, the panel said.

“Proposition 200 creates an additional state hurdle to registration,” the judges said.

The law was challenged by voting rights and Hispanic advocacy groups.

The decision is “a warning to anyone who seeks to deter or prevent voter participation” that the Constitution “will protect our democratic process,” Thomas A. Saenz, president of the Mexican American Legal Defense and Education Fund, a San Antonio-based group that argued the case, said in a statement.